In the preparation of oxygen by heating KClO3 in the presence of MnO2, only moderate heat is needed because the catalyst acts by

Correct answer: lowering the energy barrier of the reaction.

Explanation: MnO₂ acts as a catalyst by providing an alternative pathway with a lower activation energy (energy barrier). With a lower barrier, more molecules have sufficient energy to react at a given temperature, so only moderate heating is required to decompose KClO₃ to O₂.

• Lowering the pressure – Irrelevant to this solid-state decomposition.
• Increasing the surface area of the reactant – That would be a physical change to KClO₃; MnO₂ doesn’t act by simply increasing surface area.
• Increase the rate of the reaction – True, but this is the result of catalysis, not the mechanism explaining why less heat is needed. The key is the lowered activation energy.